Hi, bit late but I hope it might help.
If the reverse button is physically stuck and doesn't want to come out (I take it it's the "push-in" version, the one in the middle of the stitch length selector?), than that is due to old oil having turned into "glue". a hair dryer will help with that: you remove the top cover, it's a "pull-off design which is only held in place by catch springs over studs, and than you can the reverse mechanism from above. Bit tricky to get to (not 100% sure, but you might be able to additionally remove the side cover on the hand-crank wheel, since their bolts are usually accessible after top cover removal) but if you point the hair dryer in the general direction, it should warm up enough. Make sure to not apply too much heat! it's a solid machine, yet still has plastic parts in it!
If you're successful, the button should release. Once it's free, apply some fresh sewing machine oil to the mechanism by dripping it on to it from above.
Alternatively, you could unbolt the bottom plate since that gives you access to the mechanism from below, yet the bobbin hook and feed dog drive shafts/ push rods will be in your way.